1. Lecturer in Structural Engineering, School of Civil Engineering, Univ. of Birmingham, Birmingham B15 2TT, UK (corresponding author).
2. Senior Lecturer in Structural Engineering, Dept. of Engineering, Univ. of Cambridge, Cambridge CB2 1PZ, UK.
3. Former Senior Lecturer, Dept. of Engineering, Univ. of Cambridge, Cambridge CB2 1PZ, UK.